High Dynamic Range Photography ( HDR ) is a digital image processing technique.
Its similar to the old technique of exposure blending. The classic situation where this process is most useful is a picture that includes a dark room interior and a bright window. Take this picture with any camera and you will struggle to see detail in the overexposed window or the underexposed interior. HDR can be used in this situation to extracting extra detail from both the very light and dark areas.

For best results HDR images are created from three or more images taken at different exposures. The bright image is used to get detail from the dark areas and the dark image is used to get detail from the bright areas. The HDR image which is created has a dynamic range similar to the human eye however it is far more than can be reproduced on paper or a screen. In order for the image to be turned into something useful it is tone mapped. This process can be used to create magical Athena style images with detail in every last blade of grass.

The image on the left shows the result of combining and tone mapping three images using photomatix. The image on the right is the finished stock photo after I have adjusted the colours to give it a more natural feel. HDR images can also be produced from a single raw file as the exposure compensation has not yet been applied to the image. HDR images from a single raw file produce more noise than from multiple exposures
however if your subject is moving you may not have a choice.